Method and design of an automotive differential

ABSTRACT

A differential mechanism with offset, self-aligning spherical side gears and wider side gear separation to provide differential mechanism that is less expensive and easier to assemble.

[0001] The present invention relates generally to automotivedifferentials, and more particularly to a design for spherical sidegears, which offer an improved assembly method.

DISCLOSURE INFORMATION

[0002]FIG. 1 shows a prior art differential mechanism having an outerhousing 10 with a casing 12 rotatably supported therein on bearings 14.The casing 12 defines a chamber 16 and has a pair of diametricallyopposed openings 18 therein. A pinion shaft 20, retained by a pin 22 inthe casing 12 with one end thereof in each opening 18, transverses thechamber 16. A pair of pinion gears 24 are rotatably supported on thepinion shaft 20, one near each end, within the chamber 16. A pair ofside gears 26 retained within the chamber 16 engage the pinion gears 24to form a standard differential gear mechanism. The side gears 26 areaxially aligned with the casing 12 and constrained by the differentialgear mechanism to rotate in response to the pinion gears 24.

[0003] Each pinion gear 24 has a part-spherical end wall 24 a and issupported thereat on a correspondingly shaped inner casing wall 12 a.Similarly, each side gear 26 has a part-spherical end wall 26 a where itis supported on a correspondingly shaped inner casing wall 12 b. Theinner casing walls 12 a and 12 b define a common sphere which has aradius R and whose center coincides with the intersecting point 21 wherethe axis of rotation of the pinion shaft 20 intersects the axis ofrotation of the casing 12 or the axis of rotation of the side gears 26.It follows, therefore, that the pinion gear end walls 24 a and the sidegear end walls 26 a define a common sphere having radius R. Side gearshoulders 80, are often incorporated to hold the side gears in placewhile axle shafts 82 are inserted into the side gears. Without theseshoulders 80, the side gears 26 do not predictably remain aligned withthe axle shafts 82 to facilitate easy assembly of axle shafts. In orderto maintain side gear alignment, shoulders 80 are added to the sidegears 26 in order to speed and ease assembly operations for differentialmechanisms.

[0004] As illustrated in FIG. 2, U.S. Pat. No. 4,541,306 describes adifferential mechanism in which the side gear end walls describe twodifferent spheres, each of whose center is offset some difference fromthe differential center 21. The invention describes offsets of eachspheres centerpoint 30, toward the other spheres walls 28 a, resultingin a more narrow differential mechanism. No side gear shoulders arerequired since the offset spheres which define the inner walls willserve to hold the side gears 26 in the correct position to allowinsertion of axle shafts. This narrower differential however, has lessspace within the chamber 16, than typical differential mechanisms. Thissmaller space means that assembly operations are more time consumingsince it is more difficult to assemble the pinion gears 24, pinion shaft20 and side gears 26 in this smaller than normal space. U.S. Pat. No.4,541,306 teaches away from the present invention by claiming anddescribing spherical offsets toward opposing spherical surfaces,resulting in a narrower differential.

[0005] The prior art differential mechanisms are difficult and costly toassemble.

[0006] It would be desirable, therefore, to provide a differentialmechanism which does not require shoulders but is wide enough tofacilitate easy assembly of the differential mechanism components.

SUMMARY OF THE INVENTION

[0007] Referring to FIG. 1, the present invention overcomes thedisadvantages of the prior art approaches by providing a differentialcasing with a chamber 16, having an axle centerline 18 and defined by atleast one spherical surface 26 a and at least one opposing surface 27 a,wherein the centerpoint of the spherical surface 50 is substantiallycollinear with the axle centerline 18 and is offset from the centerpoint54 of the chamber 16 some distance along the axle centerline 18 in adirection away from the opposing surface 27 a.

[0008] The offset distance between the centerpoint 50 of the sphericalsurface 26 a and the centerpoint 54 of the chamber 16 can be effectiveeven if very small in relation to the spherical radius of the side gear26.

[0009] The present invention further overcomes the disadvantages of theprior art by providing an automotive differential mechanism comprising apinion shaft; a first pinion gear; a second pinion gear; a first sidegear, having a first side gear outer radius; a second side gear having asecond side gear outer radius; and, a differential casing having a firstaxle shaft port, a second axle shaft port, a first inner radius, a firstradius center point, a second inner radius and a second radius centerpoint, wherein the second radius center point is offset a distance fromthe first radius center point such that when the first and second piniongears, the pinion shaft and the first and second side gears areinstalled within the differential casing, the pinion gears and thepinion shaft force the first side gear outer radius into the first innerradius and the second side gear outer radius into the second innerradius such that the first side gear is substantially aligned with thefirst axle shaft port and the second side gear is substantially alignedwith the second axle shaft port.

[0010] The present invention further overcomes the prior art byproviding a differential mechanism comprising a casing adapted to berotatably driven about an axis of rotation and having a chamber definedby walls; a pair of pinion gears retained within the chamber rotatableabout an axis of rotation normal to and having an intersection pointwith the axis of rotation of the casing; a pair of side gears having apart-spherical endwall; a means for retaining the side gears fromrotating within the chamber about the axis of rotation of the piniongears including a pair of part-spherical regions defined in the chamber,each region being defined by a wall of the chamber having a sphericalshape substantially complementary to the end wall of one of the sidegears and each region providing a recess in the chamber for supportingone of the side gears; each of said side gear receiving part-sphericalregions comprising part of a sphere having a center located on the axisof rotation of the casing and offset from the intersecting point in adirection providing a chamber extending more in the axial direction ofthe casing than in the direction of the axis of rotation of the piniongears.

[0011] These and other advantages, features and objects of the inventionwill become apparent from the drawings, detailed description and claimswhich follow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a drawing of a prior art differential mechanism whichuses shoulders to position the side gears

[0013]FIG. 2 is a drawing of a prior art differential with offsetspherical centers towards respective opposing surfaces.

[0014]FIG. 3 is a drawing of the present invention illustratingspherical centers offset away from respective opposing surfaces andproviding a wider differential chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0015]FIG. 3 provides is a side view of an automotive differentialmechanism comprising a first side gear 26, a second side gear 27; and adifferential chamber 16 formed by offsetting the spherical centerpoint50 of the surface of the first side gear 26 a away from the surface ofthe second side gear 27 a along the common axis of the side gears 26 and27. Offsetting the spherical surface of even a single side gear issufficient to maintain some degree of alignment between the first andsecond side gears 26 and 27 and the axle shafts 82 during assembly.

[0016] In FIG. 3, the spherical centerpoint 52 of the second side gear27 also is offset along the common axis of the two side gears 26 and 27away from the surface of the first side gear 26. By offsetting both sidegear surfaces in this way, the side gears are capable of maintainingalignment to a very high degree with the axle shafts 82 during assemblyoperations. In addition, by offsetting both side gears in this manner, awider differential cavity 16 is formed thus allowing for easiercomponent assembly.

[0017] Offsetting these two gears in this way eliminates a need foraligning shoulders which were used in the prior art. By offsetting thecenterpoints away from each other, a wider, easier to assembledifferential mechanism results.

[0018] Various other modifications to the present invention may occur tothose skilled in the art to which the present invention pertains. Forexample, the addition of thrust washers to each side gear. Othermodifications not explicitly mentioned herein are also possible andwithin the scope of the present invention. It is the following claims,including all equivalents, which define the scope of the presentinvention.

What is claimed is:
 1. A differential casing comprising: (a) a chamber,having an axle centerline and defined by at least one spherical surfaceand at least one opposing surface, wherein the centerpoint of said atleast one spherical surface is substantially collinear with said axlecenterline is offset from the centerpoint of said chamber by an offsetdistance along said axle centerline in a direction away from saidopposing surface.
 2. A differential casing as in claim 1 wherein theratio of the radius of said at least one spherical surface to saidoffset distance is at
 30. 3. An automotive differential mechanismcomprising: (a) a first and second side gear; and (b) a differentialchamber formed by offsetting the spherical centerpoint of said firstside gear away from the surface of said second side gear.
 4. Anautomotive differential mechanism comprising: (a) a pinion shaft; (b) afirst pinion gear; (c) a second pinion gear; (d) a first side gear,having a first side gear outer radius; (e) a second side gear having asecond side gear outer radius; and, (f) a differential casing having afirst axle shaft port, a second axle shaft port, a first inner radius, afirst radius center point, a second inner radius and a second radiuscenter point, wherein said second radius center point is offset adistance from said first radius center point such that when said firstand second pinion gears, said pinion shaft and said first and secondside gears are installed within said differential casing, said piniongears and said pinion shaft force said first side gear outer radius intosaid first inner radius and said second side gear outer radius into saidsecond inner radius such that said first side gear is substantiallyaligned with said first axle shaft port and said second side gear issubstantially aligned with said second axle shaft port.
 5. An automotivedifferential mechanism according to claim 4 wherein said first andsecond side gears do not have alignment shoulders.
 6. A differentialmechanism comprising: (a) a casing adapted to be rotatably driven aboutan axis of rotation and having a chamber defined by walls; (b) a pair ofpinion gears retained within said chamber rotatable about an axis ofrotation normal to and having an intersection point with said axis ofrotation of said casing; (c) a pair of side gears having apart-spherical endwall; (d) means for retaining said side gears fromrotating within said chamber about the axis of rotation of said piniongears including a pair of part-spherical regions defined in saidchamber, each said region being defined by a wall of said chamber havinga spherical shape substantially complementary to the end wall of one ofsaid side gears and each said region providing a recess in said chamberfor supporting one of said side gears; (e) each of said side gearreceiving part-spherical regions comprising part of a sphere having acenter located on said axis of rotation of said casing and offset fromsaid intersecting point in a direction providing a chamber extendingmore in the axial direction of said casing than in the direction of theaxis of rotation of said pinion gears.
 7. A method of assembling adifferential mechanism having at least one spherical side gear, twopinion gears and a pinion shaft comprising the steps of: (a) forming acasing with at least one spherical surface substantially complementarywith a spherical surface of at least one spherical side gear; (b)inserting at least one spherical side gear into said casing so that saidspherical side gear is held in place by virtue of contact between saidat least one spherical side gear and said complementary casing sphericalsurface and the support provided by said two pinion gears and saidpinion shaft.